Anchoring hydrophilic polymer in substrate: An easy approach for improving the performance of TFC FO membrane

Abstract

A feasible protocol was designed for anchoring hydrophilic sulphonated polyethersulfone (SPES) in the PES matrix to prevent hydrophilic polymer from leaching in non-solvent-induced phase separation (NIPS) process. Montmorillonite (MMT) was introduced to interact with SPES and then blended with PES dope solution for the asymmetric substrate of thin film composite forward osmosis (TFC FO) membrane. The immobilization-effect of MMT on SPES has been examined by FT-IR and XPS analyses. The prepared substrates were characterized with respect to surface wettability (by contact angle), MWCO, pore size and distribution (by rejection of PEG and PEO) and water permeability. It was found that the water permeability of substrates was dramatically enhanced upon addition of MMT@SPES owing to the increased hydrophilicity. The pore structure of the substrates with less than 300kDa MWCO was appropriate for the formation of polyamide layer. The FO performance of resultant TFC membranes based on such substrates was evaluated in FO mode. The TFC membrane prepared using PES/SPES(40) substrate embedded with MMT exhibited 28.39 LMH osmotic water flux and 3.53g/m2h reverse solute flux with DI water as feed solution and 2.0M NaCl as draw solution and active layer facing the feed solution. Compared to the membrane based on PES/SPES substrate, the osmotic water flux of membrane with PES/MMT@SPES(40) was improved by about 4 folds when they are at similar thickness of 100µm and the reverse salt leakage reduced about the half thanks to the enhanced wettability of substrate and narrower pore size distribution of composite substrate. Based on the results, it can be confirmed that anchoring hydrophilic polymer in membrane substrate matrix is a practical method to improve the performance of TFC FO membrane.